@Override
 public String generate_code(int kind, String servers, int begin_ts, int end_ts, int n) {
   List<ActivationCode> activationCodes = new ArrayList<ActivationCode>();
   int eventId = new Long(new Date().getTime() / 1000).intValue();
   for (int i = 0; i < n; i++) {
     ActivationCode activationCode = new ActivationCode(eventId, kind, servers, begin_ts, end_ts);
     activationCodes.add(activationCode);
   }
   activationCodeDao.batch_save(activationCodes);
   return new JSONArray(activationCodes).toString();
 }